Auxiliary porting arrangement for noise control in compressor-expander

ABSTRACT

A compressor-expander for use in air conditioning having a compressor side and an expansion side with a vane-type rotor of the positive displacement type, each side having inlet and outlet ports and connected with an associated heat exchanger so that a charge of air drawn into the compressor side is compressed between adjacent vanes, cooled to remove heat of compression, and then expanded between adjacent vanes for discharge in the cold state. The compressor inlet port and expander outlet port are so positioned that the volume of an exiting charge of air is less than the volume of an entering charge of air in predetermined ratio so that air is discharged at nominally ambient pressure. At least one auxiliary equalizer port is provided in the frame of the device spaced slightly upstream of the expansion side outlet port and communicating with a region of ambient pressure so that, as an exiting charge of air approaches the outlet port, air may flow through the equalizer port with the result that the initial pressure of the exiting charge of air tends to be more nearly equalized with respect to the pressure existing at the expansion side outlet port, thereby to minimize explosive puffing of air and its attendant noise upon traverse of the vanes past the expansion side outlet port. In one embodiment of the invention the equalizer port occupies a distributed locus for spreading the equalization function over a greater angle of rotor rotation. In such event the equalizer port may consist of a diagonally arranged series of openings. In another embodiment of the invention a plurality of equalizer ports are coupled to ambient air through a conduit having an interposed muffler.

United States Patent 1 91 Edwards 1 51 Sept. 16, 1975 1541 AUXILIARY PORTING ARRANGEMENT FOR NOISE CONTROL IN COMPRESSOR-EXPANDER [75] Inventor: Thomas C. Edwards, Casselberry,

Fla.

[73] Assignee: The Rovac Corporation, Maitland,

Fla.

22 Filed: Apr. 15, 1974 211 Appl. No.: 460,755

Primary Examiner-William .l, Wye Attorney, Agent, or Firm-Wolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[57] ABSTRACT A compressor-expander for use in air conditioning having a compressor side and an expansion side with a vane-type rotor of the positive displacement type, each side having inlet and outlet ports and connected with an associated heat exchanger so that a charge of air drawn into the compressor side is compressed between adjacent vanes, cooled to remove heat of compression, and then expanded between adjacent vanes for discharge in the cold state. The compressor inlet port and expander outlet port are so positioned that the volume of an exiting charge of air is less than the volume of an entering charge of air in predetermined ratio so that air is discharged at nominally ambient pressure. At least one auxiliary equalizer port is provided in the frame of the device spaced slightly upstream of the expansion side outlet port and communieating with a region of ambient pressure so that, as an exiting charge of air approaches the outlet port, air may flow through the equalizer port with the result that the initial pressure of the exiting charge of air tends to be more nearly equalized with respect to the pressure existing at the expansion side outlet port, thereby to minimize explosive puffing of air and its attendant noise upon traverse of the vanes past the expansion side outlet port. 1n one embodiment of the invention the equalizer port occupies a distributed locus for spreading the equalization function over a greater angle of rotor rotation. In such event the equalizer port may consist of a diagonally arranged series of openings. In another embodiment of the invention a plurality of equalizer ports are coupled to ambient air through a conduit having an interposed muffler.

8 Claims, 5 Drawing Figures AUXILIARY PORTING ARRANGEMENT FOR NOISE CONTROL IN COMPRESSOR-EXPANDER In a single fluid air conditioning system using a compressor-expander device of the positive displacement type, and in which the air itself serves as the coolant, explosive puffing of air at the expander outlet port, when exhaust pressure differs slightly. from ambient pressure, creates an inherent noise. problem. Even.

where a system is carefully designed, by reason of.

proper port placement and the like, to exhaust at ambient pressure, the design conditions including ambient pressure, temperature and humidity, as well as leakage and variation in driving speed, are unfortunately subject to constant change,- resulting in a pressuredifferential, and hence noise.

It is, accordingly, an object of the present invention to provide simple and effective means for minimizing noise produced in a single fluid compressor-expander. It is a more specific object to provide, in such a device, an auxiliary equalizer port spaced just ahead of the ex pansion side outlet port for equalization of the pressure prior to discharge of the air through the outlet port. It is a general object of the invention to provide means for inhibiting the production of noise in a compressorexpander which may be economically incorporated at little or no added cost and whichcompensates for anyv change in the ambient or operating conditions constantly and without adjustment.

Other objects and'advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which: 4

FIG. I is a diagrammatic fragmentary cross section of a refrigeration unit of the co'mpressorexpander type.

FIG. la is a general view of the refrigeration'unit at reduced scale and showing the associated heat .ex-

changer.

FIG. 2 is a fragmentary view taken along the line 22 in FIG. I.

FIG. 3 is a view similar to FIG. I but showing an aI- ternate construction.

FIG. 4 is a fragmentary view 44 in FIG. 3. I

While the invention has been described in connec tion with certain preferred embodiments, it will be un derstood that I do not intend to be limited by the particular embodiments shown, but I intend, on'the contrary, to cover the various alternative and equivalent forms of the invention included within the spirit and scope of the appended claims.

Turning now to FIGS. 1 and 1a there is shown an air conditioning unit 10 of the compressor-expander type having aframe or stator 11 in which is mounted a rotor 12 on a shaft 13, the ends of the shaft being journaled in suitable end members (not shown). The shaft is rotated, in the direction'of the arrow, by suitable driving means 14. Slidably mounted in the rotor are vanes 21-30 inclusive.

As shown the left-hand side, referred to as the com pressor" side has an inlet port 31 and an outlet port 32. The right-hand or expansion side hasan inlet port 33 and an outlet port 34. Ducts 35, 36 provide communication with the'respective-ports'3l, 34.-

All of the vanes are pressed outwardly into effectiveengagement with the interior wall 37 of the frame 11 by means of a spring band 38. Adjacent vanesthus delooking along the line changer 40 is used having an inlet 41 and outlet 42 and a plurality of heat exchanging fins 43. For further details reference may be made to my prior US. Pat. No. 3,686,893 which issued on Aug. 29, 1972 and my appli' cation Ser. No. 400,965 filed Sept. 26, I973. The profile of the inner wall 37 of the frame is preferably of ovalconfiguration. Thus as the rotor rotates in the direction shown, a typical compartment, indicated at 51 and defined by vanes 21, 22, increases in volume, with air being drawn in through the inlet port 31 until vane 21 reaches the end 52 of the inlet port, at which time the compartment has an entering charge of air at substantially atmospheric pressure. The volume of such entering charge is proportional to the projected area of the compartment which has been indicated by crosshatching A in FIG. 1a.

The air in the compartment Slis progressively compressed and squeezed, at high pressure, through the compressor outlet port 32 into the heat exchanger 40 where the heat of compression is given off.- The air passes through the heat exchanger at substantially constant pressure, flowing, while still at high pressure, into the expander inlet port 33. As the rotor continues its rotation, taking the compartment 53 between vanes 27,

' 28 as typical, the vane 28 will reach the threshold 54 of the outlet port 34, which is the condition illustrated in FIGS. 1 and la. The exiting charge of air in compartment 53 has a volume which is indicated by the crosshatched area B. As a matter of design, the end 52 of the inlet port and the beginning 54 of the outlet port are so positioned that the volume of a cold dense exiting charge of air is less than the volume of an entering charge of air in such ratio (area B to area A) that the masses of air are the same in both compartments 52, 53. Under such circumstances the air will be discharged at substantially the same pressure as it was taken in, that is, at ambient pressure. While discharge of the air at ambient pressure has been recognized as desirable it is not possible to design in this condition with precision, particularly in the face of a change in operating conditions. For example, where conditions are such that an exiting charge of air in the compart ment 53, as it is about to be discharged (FIG. la), is at a pressure which is higher than ambient, that is, higher than that which exists at the discharge side of the outlet port 34, an explosive outward puff will occur as the vane 28 clears thethreshold 54 of the outlet port. A similar explosive puff will occur upon passage of the next vane 27, and this is repeated for each vane at a cyclic rate which is ten times greater than the speed of rotation of the shaft (there being ten vanes). The result is noise in the form of a sonic vibration having a pitch which depends uponthe driving speed and which has an amplitude whichdepends upon the pressure differential. Indeed, production of noise tends to be rather efficient since the mechanism of its production, chopping of an air stream at a discharge port, is similar to that of a'siren. I

However, in accordance with the invention an auxiliv iary equalizer port is provided in the frame 11 spaced slightly upstream of the expansion side outlet port and communicating with a region of ambient pressure so that as the vanes transport an exiting charge of air toward the outlet port, air may flow through the equal izer port so that the initial pressure of the air is more nearly at ambient level. Further in accordance with the invention the equalizer port may be in the form of a plurality of openings which are progressively spaced from the outlet port so that equalization occurs pro gressively, the openings preferably being arranged along a diagonal path. Thus, referring to FIG. 1 and 2, there is provided, spaced upstream, that is, clockwise,

from the outlet port 34, an auxiliary or equalizer port in the form of a diagonal row of openings 60. Such openings are, as shown in FIG. 2, arranged along a single generally linear path, with the first opening 61 of the series being spaced from the outlet port at distance S1 while the closest opening 62 is spaced at'a distance S2. Thus the oncoming vane, defining a typical exiting charge of air, first uncovers the opening 61 to begin the equalizing process. The remaining openings in the series are progressively uncovered, with a small amount of air passing through each of them. Thus as the vane arrives atthe outlet port, the initial discharge pressure of the exiting charge of air is substantially equal to the ambient pressure so that any explosive puff is avoided; instead the air is silently squeezed out of the compartment into the region of ambient pressure.

It will be understood that the term region of ambient pressure" is a general onereferring to any region which is at or near the pressure at the discharge side of the outlet port which is in direct communication with the air conditioned space.

The holes which comprise the equalizer port 60 are preferably of limited diameter so that the air which passes therethrough, in one direction or the other depending upon the pressure differential, is slightly throttled. For additional throttling the equalizing port may terminate in a small diameter conduit or may be fitted with an adjustable throttling valve.

In any event, the equalizer port preferably discharges into a space which is isolated from the cooled space, that is, isolated from the duct 36 as illustrated in FIG. 1. One advantage of isolating the equalizer port is that the compressor-expander unit is customarily located in a space which is separated from, and often remote from, the space into which the cooled air is discharged. For example, in an automotive installation, with the unit under the hood, the equalizer port may discharge directly into the atmosphere. Thus any noise originat ing at the equalizer port openings will not be directly transmitted through the duct 36 into the interior of the automobile. If it is desired, on the other hand, to couple the equalizer port to the main port for common discharge, the wall 36 (FIG. 1) may be moved slightly to the right.

In accordance with one of the aspects of the present invention the equalizer port, spaced slightly upstream from the outlet port, instead of being vented directly to a region of ambient pressure, is connected to a conduit which includes a muffler for muffling the sound energy. Thus referring to FIGS. 3 and 4 an alternative embodiment is shown in which corresponding elements are indicated by corresponding reference numerals with addition of subscript a. In this embodiment a rotor 12a. having the usual vanes and journaled in the frame lla discharges cold air through an outlet port 340 having a threshold 54a. Spaced slightly upstream from the port 34a is an equalizer port 600 formed of a row of openings, of which typical openings are indicated at 61a,

62a.-Connecting allof the openings together is an axially extending bore or header" 63 which communicates with conduits 64 equipped with sonic mufflers 65 discharging at 66. The sonic mufflers do not, per se, form a part of the present invention and it will be undcrstood that such members are conventional andpreferably tuned to attenuate soundwaves at-a frequency corresponding to the frequency of vane arrival which,

in the present instance, is ten times the shaft speed. As

a result of the use of the mufflers 65 the air which exits at 66 will have little residual sound energy. While it is convenient, in understanding the invention, to think of air flowing through the conduits as in the direction shown by the arrows in FIG. 4, it will be understood that the present arrangement is equally effective to prevent noise regardless of whether the pressure ofthe charge of exiting air is greater or less than the pressure of the ambient air in the duct 36. One advantage of the embodiment shown in FIGS. 3 and 4 is that the equalizer port may be axially instead of diagonally arranged, which contributes'to the simplicity of the construction,

the resulting abruptness of the equalization being ade-.

quately taken care of by-the mufflers. While two conduits and two mufflers are illustrated in FIG. 4, it .will

be understood that one such conduit and muffler may, if desired, be dispensed with. It will also be understood that the equalizer port in FIGS. I and 2 may be similarly muffled and that such port may if desired be in the form of a continuous diagonal slot having about the same total area as the individual drilled openings.

In any event the use of equalizer ports constitutes a simple solution to a problem which is inherent in devices of this type. t

The term vanes as used herein will be understood to broadly include any partition means defining chambers which are progressively compressed in size, and enlarged, for the compressor andexpander functions. The term region of ambient pressure as used herein refers to any region which is external to the pressurized compartments defined by the vanes and where normal or near normal atmospheric pressure exists, including the expansion side outlet port, so thatleakage to or from such region through the equalizer port precludes any substantial pressure difference between compartment pressure and outlet port pressure at the moment a vane uncovers the expansion side outlet port.

What I claim is: 1. In a refrigeration system the combination comprising a compressor-expander includinga frame defining chamber means having a compression side and an expansion side, a vane type rotor means mounted in the chamber means for positive displacement of air in the form of entering and exiting. charges, the frame defining compressor side inlet and outlet ports as well as expansion side inlet and outlet ports, a heat exchanger connected between the compressor side outlet port and the expansion side' inlet portsorthat upon driving of the rotor means air drawn into the compressor side is (l) pressure of the exiting charge of air with the pressure existing at the expansion side outlet port, thereby to minimize explosive puffing of air and its attendant noise upon traverse of the vanes past the expansion side outlet port.

2. The combination as claimed in claim 1 in which a duct is provided for conducting cold air from the outlet port to a compartment to be cooled and in which the equalizer port is isolated from such duct so that any noise generated by reason of flow of air through the equalizer port is isolated from the compartment.

3. The combination as claimed in claim 1 in which a plurality of auxiliary equalizer ports are provided spaced slightly upstream of the expansion side outlet port and having progressive amounts of spacing therefrom.

4. The combination as claimed in claim 2 in which the auxiliary equalizer ports are arranged in a diagonal row.

5. The combination as claimed in claim 1 in which the equalizer port is connected to the region of ambient pressure by a conduit providing a throttling restriction.

6. The combination as claimed in claim 5 in which the conduit includes a sonic muffler of a size in proportion to the flow through the conduit.

7. The combination as claimed in claim 1 in which the outlet port is in the form of closely spaced rows of holes in the frame and in which the equalizer port is in the form of a first row of holes on the upstream side, the first row of holes being connected to the region of ambient pressure.

8. The combination as claimed in claim 7 in which the holes in the first row are interconnected by an axially arranged header and in which a muffler is provided having its inlet connected to the header. 

1. In a refrigeration system the combination comprising a compressor-expander including a frame defining chamber means having a compression side and an expansion side, a vane type rotor means mounted in the chamber means for positive displacement of air in the form of entering and exiting charges, the frame defining compressor side inlet and outlet ports as well as expansion side inlet and outlet ports, a heat exchanger connected between the compressor side outlet port and the expansion side inlet port so that upon driving of the rotor means air drawn into the compressor side is (1) compressed between adjacent vanes, (2) cooled in the heat exchanger to remove the heat of compression, and (3) expanded betweEn adjacent vanes for discharge in the cold state, the chamber means having an auxiliary equalizer port spaced just slightly upstream of the expansion side outlet port and communicating with a region of ambient pressure so that, as a vane confining an exiting charge of air approaches such outlet port, air flow through the equalizer port tends to equalize the pressure of the exiting charge of air with the pressure existing at the expansion side outlet port, thereby to minimize explosive puffing of air and its attendant noise upon traverse of the vanes past the expansion side outlet port.
 2. The combination as claimed in claim 1 in which a duct is provided for conducting cold air from the outlet port to a compartment to be cooled and in which the equalizer port is isolated from such duct so that any noise generated by reason of flow of air through the equalizer port is isolated from the compartment.
 3. The combination as claimed in claim 1 in which a plurality of auxiliary equalizer ports are provided spaced slightly upstream of the expansion side outlet port and having progressive amounts of spacing therefrom.
 4. The combination as claimed in claim 2 in which the auxiliary equalizer ports are arranged in a diagonal row.
 5. The combination as claimed in claim 1 in which the equalizer port is connected to the region of ambient pressure by a conduit providing a throttling restriction.
 6. The combination as claimed in claim 5 in which the conduit includes a sonic muffler of a size in proportion to the flow through the conduit.
 7. The combination as claimed in claim 1 in which the outlet port is in the form of closely spaced rows of holes in the frame and in which the equalizer port is in the form of a first row of holes on the upstream side, the first row of holes being connected to the region of ambient pressure.
 8. The combination as claimed in claim 7 in which the holes in the first row are interconnected by an axially arranged header and in which a muffler is provided having its inlet connected to the header. 